The incidence of M. avium infection (MAI) in the SAIDS colony has grown steadily in the past four years. This opportunistic infection produces diarrhea, cachexia, and sometimes pneumonia in severely immunocompromized monkeys with remarkable similarity to MAI in children with AIDS. We are developing expertise in antemortem identification of this infection by culture and PCR to support immunologic studies of natural defense statigies against mycobacteria including amplification of lymphocyte subsets and cytokine activation of immune cells. We have derived mycobacterial isolates from the environment (soil and water) and monkeys for molecular fingerprint analysis to characterize the epidemiology of MAI.